Heat exchanger



w. A. SHAW HEAT EXCHANGER Filed Maron 19, 1942 Feb. 16, 1943.`

Patented Feb. 16, 1943 HEAT EXCHANGER Wilbur A. Shaw, Forest Hills, N. Y., assignor to American Locomotive Company, New York, N. Y., a corporation of New York Application March 19, 1942, Serial No. 435,315

2 Claims.

This invention relates to heat exchangers, and more particularly to jet-type exchangers.

The present invention is directed to increasing the heat transfer rate of an exchanger so that a smaller exchanger can be employed to do the same amount of work ordinarily done by a larger exchanger. For example, the exchanger shown in the drawingforming a part of this application is a jet-type lube oil cooler adapted for employment with a Diesel engine. It is de sirable to keep the exchanger as small as pos sible so that it can be conveniently mounted on the Diesel engine, forming an auxiliary thereof. It functions to cool the lubricating oil after a lubricating cycle. The present invention has application, of course, to jet-type exchangers designed for other purposes. However, for simplicity, the following description will be restricted to the lube oil cooler as shown.

It is a fact well known in the heat exchange art that laminar flow of a liquid over the outside of the tubes of a tube bank produces a stagnant lm of liquid adhering tc the outer surfaces of the tubes, This nlm is of a thickness proportional to the velocity of flow of the liquid; between the tubes there is a flow of essentially parabolic velocity distribution. The aforementioned nlm resists the transfer of the heat between fluid inside of the tubes and the liquid outside, with a resultant decrease in transfer rate. If the tubes are iin tubes, and thus necessarily spaced farther apart than plain tubes, the free cross-sectional area for `flow between the tubes is greater, resulting in lower velocities and lower transfer rate.

An object of the present invention is to provide a heat exchanger having means for minimizing film formation, thereby increasing transfer rates.

A further object is to provide in an exchanger of the aforesaid characteristics means producing small net free flow areas at intervals in the shell thereof, thereby increasing velocity of, and creating turbulence and remixing in, the iiow through the shell.

A further object is to provide an exchanger which can be made in a smaller size than conventional design to handle the same heat duty,

Other and further objects of this invention will appear from the following description, the accompanying drawing and the appended claims.

Referring to the drawing forming Va part of this application, Figure 1 is, at the left, a plan view of an exchanger embodying the present invention, and at the right the cover is removed,

a portion of the tube sheet is broken away and the baffles and tube exposed are shown in section on a line taken through the upper perforations; Fig. 2 is, at the left, a side elevation of the exchanger, the fins on the tubes not being indicated, and at the right a section on the line II-II of Fig. 1, parts being shown in full, some iins being shown and the remainder of the finned area being indicated by dot and dash lines; Fig. 3 is a section on the line III- III of Fig. l, fins being shown and indicated as in Fig. 2; and Fig. 4 is a fragmental plan View of a Inodied heat exchanger, the tube sheet and cover being removed and the baffles and tubes being shown in section on a line taken through the upper perforations.

The lube oil cooler is indicated generally by the reference numeral I. It includes a welded built-up shell 2. box-shaped and open at the upper end, a bolting flange 3 being welded around the upper edge. The shell has a front wall 4 provided with an inlet 5 formed by a nozzle welded in a port in wall 4, and a rear wall 6 provided with an outlet 'I formed by a nozzle welded in a port in wall t. The shell further includes side walls 8.

A series of parallel spaced perforated shellpartitioning baiiles 9 are disposed in the shell, extending between and welded to the side walls 8, and being at their bottoms welded to the bottom Wall IQ of the shell. Tlie tops of the baffles are flush with the top of the bolting flange 3. An inverted V-cut II is formed in the bottom of each baille to allow complete drainage through drain openingr I2 when desired. Opening I?. is ordinarily closed by plug I3. A shell vent le, closed by a plug I5, is provided in the bolting flange 3.

The baiiles 9 are equally spaced from each other. IIhe front baffle is spaced from the wall li and the rear baiiie from the wall 6. Each baille has four vertical rows of vertically extending slot-shaped periorations I6. These perforations are so shaped and proportioned as to provide the desired reduced free area for ow through the shell from the inlet to the outlet, and are sufficiently restricted to jet the liquid iiowing through them, for a purpose presently 4 ring-shaped, covering only the flange, or it may cover the entire bottom face of the tube sheet,

having orifices in line with tube sheet orices, and being engaged by the baffles to seat their upper edges. The tube sheet has a row of orices I9 adjacent `one wall 8, there being one orice between. each adjacent pair of baiiles, and a similar row of orifices adjacent the other wall 8.

A U-bend tube 2l, formed of a row of straight legs connected progressively by U-bends, is disposed between each adjacent pair of bailies with the planes of the baffles and rows of legs par-V allel. Each tube 2I has an inlet leg 22 expanded at its free end in the adjacent orifice 20 and depending into the shell. Leg 22 is connected by a U-bend 23 to an upwardly extending leg 24, the U-bend being in the bottom of the shell. Leg 24 is connected by a U-bend 25 to another downwardly extending leg 2E, U-bend 25 being disposed in the shell adjacentV tube sheet II. Leg 26 is connected by a Ll-bend 21, at its lower end, to an upwardly extending outlet leg 28 which is expanded at its upper free end in the adjacent orifice I9. U-bend 21 is disposed similar to U-bend 23. Each leg has secured to its outer face radial horizontal ns 29. Other types of fins may be employed, however, and it has been found that a continuous helical iin is well suited for use in the cooler I. In Figs. 2 and 3 the fins are only shown at the top and bottom of the straight portions of the legs. However the entire straight portions of all legs in the cooler are nned, this being indicated in Figs. 2 and 3 by vertical dot-dash lines a.

The legs of the U -bend tubes are disposed with their axes in line with the adjacent rows of perforations, as is shown in Fig. 3. That is to say, all the legs 22 and the adjacent perforations of the baiiles are in the same Vertical plane. This is also true of the other legs.

A cover 3i) is supported on top of the tube sheet by means of a bolting flange 3l having orifices in line with the adjacent tube sheet and belting flange 3 orices. A gasket 32 is disposed between flange 3I and the tube sheet. Bolts 33 secure the cover, tube sheet and shell together, the cover and the tube sheet together forming a header, the tube sheet forming the bottom wall of the header and closing the open upper end of the shell.

The header is divided into an inlet compartment 34 and an outlet compartment 35 by a partition 3S which is supported by the cover 3Q end sealed against the tube sheet by a gasket 3'? which may be made as part of gasket 32 if desired. Cover is shown as a casting, although it may be built up if desired. It has an inlet nozzle 38 opening into compartment 34 and an outlet nozzle 38 opening into compartment All the legs 22 open into compartment 34 all the legs 2i! open into compartment 35.

The operation of the cooler I is as follows: Hot lubricating oil from the Diesel engine enters shell 2 through inlet 5, entering the space between wall 4 and the first baille 9. As the oil is under pressure, say for example forty pounds, it is forced through the perforations IB. As the perforations are axially in line with the legs of the first U-bend tube 2|, the oil is jetted directly on the legs. The perforations are so proportioned and shaped that the oil iiows therethrough and impinges against the legs under considerable velocity, which velocity and irnpingement minimizes lm stagnation on the legs, wiping off any that may have formed, causes turbulent flow between adjacent baffles, and effects an increased heat transfer rate between the oil and the iiuid in the tubes, which in the instant case will be cooling water. The turbulence furthermore causes a mixing of the oil providing uniform cooling.

The cooling Water enters the header through inlet nozzle 33. It flows from compartment 34 simultaneously into all legs 22, legs 22 thus being arranged for parallel flow. The legs of any one tube are arranged for series ow. The cooling water thus enters each tube at the same temperature. However, the temperature in the outlet legs 28 varies successively from the front to the rear of the shell, being hottest at the front. Legs 28 expel the heated water into outlet compartment 35.

The oil, as aforesaid, is impinged directly on the legs of one tube, so that hot oil of uniform temperature passing through the rst baliie is treated by cooling water in a single tube, the water naturally being cooler in the inlet leg than in the outlet leg, as aforesaid.

The first baffle effects only a slight drop in pressure in the oil, so that the oil passes through the perforations of the second baffle and is jetted against the second U-bend tube. This operation is repeated until the oil passes out of outlet 'i in a cooled state. Thus the oil has series flow through the baiiies and is treated in series by the tubes. Each' time the oil passes through a baffle it is cooler. Each of the U-bend tubes is receiving water at uniform low temperature, as aforesaid, so that the oil is always treated by cold water between adjacent baffles, there being no U-bend tube between baffles which receives water heated by a previous step in the heat transfer.

The oil flows through the shell longitudinally thereof, the length "of the shell being determined by the direction of flow of shell liquid, and the water ows through the tubes transversely of the shell. There is no longitudinal water flow. This enables the legs of a U-bend tube to be disposed entirely between two adjacent baffles, as shown, the U-bend tube thus being removable from the shell without disturbance of the baies. Thus, when it is desired to clean the fins or shell, it is only necessary to remove bolts 33 and lift the tube sheet and U-bend tubes as a unit from the shell with its baffles. 'Ihis is an important advantage of the present heat exchanger.

'Ihe modified heat exchanger of Fig. 4 is like the cooler I except that the baffles 40 have louvreshaped perforations 4I. These are formed by making, for each perforation, a single straight cut in the baille and forcing the metal at one side of the cut out into the louvre shape. Th-e iiow through a row of louvres will be inclined to the baffle. Therefore to induce the desired irnpingement the row is disposed at one side of its correlated tube leg land parallel to the axis thereof. The disposition of the rows of louvre-shaped perforations is clearly shown in Fig. 4, the inlet 42 in this exchanger being at the right, the two inner rows of /Derforations being side by side and oppositely directed. The operation of the cooler of Fig. 4 issimilar to the cooler I.

The heat exchanger of the present invention, as aforesaid, may be employed otherwise than as a cooler and with other fluids than those described. Furthermore, the perforated bafiies may be made in other ways. For instance, the perforations I6 might be joined to form one long continuous slit.

The baffles perform two main functions. First, they reduce the net free flow area of the exchanger in that the shell liquid must flow through a smaller area to pass from tube to tube than it would were no baies employed, the net free iiow area in such case being that not occupied by the U-bent tube. Second, the periorations cause a jet flow against the tubes. Both the decrease in net free ow area, which increases velocity, and the jetting, effect increases in heat transfer rate.

The bales, as aforedescribed, are arranged across the shell liquid flow from the shell inlet to the shell outlet for series ilow through the baffles. There is a bafe in front of the first U-bent tube and a bafe after the last U-bend tube. However, if desired, there may be a U-bend tube in the space between wall 4 and the adjacent baffle and in the space between Wall 6 and the adjacent baflie, these spaces in such case being made of a suitable Width for this.

While there have been hereinbefore described approved embodiments of this invention, it will be understood that many and various changes and modifications in form, arrangement of parts and details of construction may be made thereto without departing from the spirit of the invention, and that all such changes and modifications as fall within the scope of the appended claims are contemplated as a part of .this invention.

The invention claimed and desired to be secured by Letters Patent is:

l. A heat exchanger comprising a shell having an open end and an inlet and an outlet port; a header secured to said shell, closing said open end, and having a tube sheet and ported inlet and outlet compartments; parallel spaced perforated shell-partitioning baiiies disposed in said shell for series flow therethrough of fluid under pressure; and U-bend 1in tubes in said shell, each having its free ends secured in sai-d tube sheet, opening respectively into said inlet and said outlet compartments, and being formed of a row of straight legs connected progressively by U-bends, each tube being disposed adjacent a baffle at the outlet shell port side thereof and having its plane parallel thereto, the perforations of said adjacent baffle being arranged in rows, a row being parallel and adjacent to each leg of said adjacent tube, theperforations thereof being shaped and proportioned to jet shell fluid against said adjacent leg, said perforations providing series flow through said baffles.

2. A heat exchanger comprising a shell having an open end and an inlet and an outlet port; a header secured to said shell, closing said operi end, and having a tube sheet and ported inlet and outlet compartments; parallel spaced louvred shell-partitioning bales disposed in said shell for series ow therethrough of iluid under pressure; and U-bend fin tubes in said shell, each having its free ends secured in said tube sheet, opening respectively into said inlet and said outlet compartments, and being formed of a row of straight legs connected progressively by U-bends, each tube being disposed adjacenta baille at the outlet shell port side thereof and having its plane parallel thereto, the louvres of said adjac-ent vbaffle being arranged in rows, a row being parallel to and offset to one side of each leg of said adjacent tube with the louvre openings extending lengthwise axially of and directed toward said leg, said louvres being shaped and proportioned to jet shell fluid against said adjacent leg, said louvres providing series flow through said bailies.

WILBUR A. SHAW. 

